Learn what context poisoning is, how to recognize it in a Bob conversation, and how to recover by starting a fresh task or improving context hygiene.

About context poisoning

Context poisoning is when wrong or irrelevant information gets into the context window and stays in the transcript. Bob treats the information as fact on follow-up prompts. Replies drift. Tool calls become inaccurate. The work goal gets lost.

This is different from a single bad answer. The bad data sits in Messages (or came in through a file read, log paste, or outdated comment). Bob re-sends it on every prompt until you reset or condense.

For how the window fills and when to start fresh, see Context window management. For a hands-on reset walkthrough, see Create a new context window.

Symptoms

You are likely dealing with context poisoning when you notice any of the following:

Worse output: Suggestions repeat, wander, or stop matching the repo.

Wrong tool use: Tool steps in the transcript no longer match what you asked for.

Stuck multi-step work: Long multi-prompt flows loop or stall.

Short-lived fixes: A corrective prompt helps once, but then the problem returns.

Tool confusion: Bob misuses tools even though Tool definitions did not change.

If Messages is already large, check the context window breakdown first. Poisoning and an overfull window often occur together.

Common causes

Cause	What happens
Bad facts in the thread	Bob states something incorrect. Later exchanges treat it as ground truth in Messages.
Stale or wrong repo text	Outdated comments, README fragments, or generated docs mislead file reads.
Oversized pastes	Logs or snippets with noise, truncation, or hidden characters land in Messages.
Condensation	Bob summarizes older Messages. Useful detail disappears. What remains can dominate the thread.
Irrelevant context	Unrelated files, old plans, or a prior work goal still exist in the transcript.

Once bad context is in Messages, it persists across every subsequent prompt. Bob does not reliably ignore plausible text just because it is wrong.

Limitations of corrective prompts

Pasting Tool definitions, rules, or a strict corrective prompt into the conversation might mask the problem for one or two exchanges. The poisoned Messages history is still there. The next off-topic question can bring the same failure back.

The reliable fix is a new task: click + (New Task) in the chat panel. See Create a new context window.

Recovery

Start a new task with + (New task). This clears poisoned Messages while keeping Rules and project files on disk.

Paste less. Send only the log lines or errors Bob needs. Large dumps increase Messages and introduce more risk.

Split the work goal. Use separate tasks for unrelated steps so that a stale transcript does not carry over.

Check tool output. If a tool returns garbage, stop and reset rather than letting Bob build on it in Messages.

Trust tests over text. When comments and code disagree, point Bob at runnable checks. This is the same guidance as context window best practices.

Prevention

Most prevention is a result of good context hygiene:

Scope the work goal before repo exploration (context window management).

Keep AGENTS.md and Rules short and operational.

Add files and logs when needed, not up front.

Reset when Messages grows without progress.

For repo-wide reads, use subagents so that the task sees subagent results, not every tool step in Messages.

Learn more

Context window management

Create a new context window

Context poisoning